Sadness
Sadness is an emotion marked by low energy and pain. It's usually bound to some event that causes it, but it can also be spontaneous, as a normal aspect of the mind, or surfaced by health conditions.
It can have a role in reflection, grief, recollection and closure over something that impacts us negatively -- be it a significant life event or a momentary burst of emotion. It can also signal that we are being wronged or misunderstood.
Despite its importance in creating the context for self-reflection and processing of negative feelings, prolonged dwelling in sadness tends to be a sinking, cyclic experience that may not have a path out of itself at all.
Sadness can reinforce our tendency to put ourselves before others. This is a defensive feature that may play an important role in situations where our needs need centering, but it may also end up serving as an excuse for abuse or neglect.
A major component that motivates sadness can be feelings such as shame, guilt and worthlessness. These feelings are also self-centered, and may be used to empower the self by arming it with feelings of being wronged or deserving of pity.
Compassion is a major tool when counteracting sadness. Compassion for oneself displaces self-directed feelings such as anger, shame and guilt. Compassion for others can help understand their angle in a situation and open avenues of communication, which in turn can dispell sadness through catharsis or consensus towards a renewed intention. Not restricting compassion only to oneself or the other, one also avoids being fooled into passive, deceiving compassion.